Implantable medical devices are often configured to be used in conjunction with an external programmer that allows a physician to display information detected by the implanted device. For example, the external programmer may operate to display electrical cardiac signals detected by the implantable device in the form of IEGMs. An IEGM is representative of electrical signals emitted by active cardiac tissue as detected by electrodes placed in, on or near the heart. The electrical signals are digitized and recorded within the implanted device along with an indication of the date and time, and are ultimately transmitted to the external programmer for display thereon, typically during follow-up sessions with the physician sometime after the device has been implanted.
The implanted device may also be configured to detect various events within the electrical cardiac signals, such as atrial depolarization events (P-waves), ventricular depolarization events (R-waves), ventricular repolarization events (T-waves), premature atrial contractions (PACs) and pre-ventricular contractions (PVCs), and to generate event codes representative of the events for transmission to the external programmer. The events are detected and event marker codes are stored in the implanted device along with the corresponding IEGM signals for subsequent transmission to the external programmer. The external programmer generates event marker icons based on the event code and displays the icons along with the IEGM signals and surface EKG signals. Exemplary event markers are: “P” for a sensed depolarization event in the atria; “R” for a sensed depolarization event in the ventricles; “A” for a paced depolarization event in the atria, and “V” for a paced depolarization event in the ventricles. Along with the event markers, the programmer may also display variable length horizontal lines representative of the length of atrial and ventricular refractory periods associated with certain events, as well as numerical values indicative of heart rate and indicative of various measured intervals between atrial and ventricular events, based on still further information recorded and transmitted by the implantable device.
Displays of IEGMs and corresponding event markers are helpful in permitting the physician to diagnose arrhythmias and to program the implanted device to provide optimal therapy. U.S. Pat. No. 5,431,691 to Snell et al. entitled “Method and System for Recording and Displaying a Sequential Series of Pacing Events” provides a description of the operation of an exemplary pacemaker and external programmer including a detailed description of the generation, transmission and display of IEGM data and event markers. See, also, U.S. Pat. No. 6,633,776 to Levine, et al., entitled “Method and Apparatus for Generating and Displaying Location-Specific Diagnostic Information using an Implantable Cardiac Stimulation Device and an External Programmer.” Herein, IEGMs, corresponding event markers and any other pertinent data stored therewith is collectively referred to as “IEGM data.”
Current state-of-the-art devices permit IEGMs to be sensed and recorded using several possible electrode configurations. For example, one IEGM may be derived from voltage signals sensed between the right ventricular (RV) tip electrode and the RV ring electrode; whereas another IEGM may be derived from voltage signals sensed between the right atrial (RA) tip electrode and the housing or “can” of the device itself. Each electrode combination thereby provides a different “view” of the electrical conditions of the heart, which is particularly helpful to the physician. In this regard, if the patient is subject to atrial arrhythmias, it may be advantageous to specifically examine atrial IEGM data, such as the aforementioned AR TIP-can IEGM; whereas, if the patient is subject to ventricular arrhythmias, it may instead be advantageous to examine ventricular IEGM data, such as the aforementioned VR TIP-VL TIP IEGM. Lead systems often include numerous electrodes, thereby providing a wide range of choices of electrode pairs for recording IEGMs. In addition to the aforementioned AR TIP, VR TIP, VL TIP and device housing electrodes, lead systems for use with state-of-the-art devices may include: a right atrial ring electrode (AR RING), a left ventricular tip electrode (VL TIP), a left atrial ring electrode (AL RING), a left atrial coil (AL COIL), a right ventricular coil (RV COIL), a left ventricular tip electrode (VL TIP), a left ventricular ring electrode (VL RING), left ventricular coil (VL COIL). Typically, IEGMs that are sensed between the device housing and one of the electrodes implanted on or within the heart, such as between the VR TIP and the device housing, are referred to as “unipolar” IEGMs. IEGMs sensed between a pair of the electrodes both implanted on or within the heart, such as between the VR TIP and the VR RING, are referred to as “bipolar” IEGMs.
As can be appreciated, given memory and power limitations within an implantable device, it is not typically feasible to sense and record IEGM data from every possible pair or electrodes. Accordingly, physicians are invited to select particular electrode configurations for recording IEGM data of particular interest. For example, the physician may select two atrial channel IEGMs (i.e. IEGMs derived primarily from atrial electrodes) and two ventricular channel IEGMs (i.e. IEGMs derived primarily from ventricular electrodes) for recording. Moreover, it is not ordinarily feasible to record each of the selected IEGMs at all times. Rather it is typically feasible only to record IEGMs and corresponding event markers during periods of interest, such as during an arrhythmia. Accordingly, state-of-the-art devices are configured to record the selected IEGM data only in response to the detection of arrhythmias or other anomalous events of interest (PACs, PVCs, etc.), or following an automatic mode switch (AMS) from one pacing mode to another. The events triggering the recording of IEGMs are referred to as “triggers.” In state-of-the-art devices, the physician is invited to select the particular triggers to be used by the device in activating the recording of the IEGM data. With current state-of-the-art devices, once any particular selected trigger is detected by the device, each of the selected IEGMs is then sensed and recorded along with the event records containing corresponding event makers.
In many cases, it is also desirable to record IEGM data prior to the trigger, as well as just following the trigger, so that the physician can review the conditions leading up to the trigger. This is particularly important insofar as arrhythmias are concerned as the physician usually wants to be able to review IEGM data prior to the onset of the arrhythmia so as to more readily diagnosis the cause of the arrhythmia. Accordingly, many state-of-the-art devices are configured to allow so-called “pre-trigger IEGMs” to be saved along with IEGMs recorded during an arrhythmia. Briefly, the device continuously detects and records IEGMs in a circular first-in/first-out (FIFO) queue. If an arrhythmia is detected, the IEGMs recorded just prior to the onset of the arrhythmia are transferred from the FIFO queue to long-term memory, so that the pre-trigger IEGMs can be saved along with IEGMs recorded during the arrhythmia itself for subsequent review by the physician. In this manner, IEGMs detected during the period of time leading to the onset of the arrhythmia is saved in long-term memory for subsequent review by the physician, without requiring all IEGMs to be saved in long-term memory at all times. Pre-trigger IEGMs can also be transferred to long-term memory upon detection of other selected triggers, such as pacemaker mediated tachycardias (PMTs), PVCs, AMS events, etc. A particularly effective technique for implementing pre-trigger memory is set forth in U.S. patent application Ser. No. 10/782,684, of Kroll, filed Feb. 18, 2004, entitled “System and Method for Controlling the Recording of Diagnostic Medical Data in an Implantable Medical Device.”
Thus, state-of-the-art devices provide for the recording of pre-trigger and post-trigger IEGMs upon detection of particular diagnostic triggers chosen by the physician or other clinician. Moreover, the physician or other clinician can also specify the particular IEGM “views,” i.e. the particular electrode pairs for use in sensing the IEGMs to be recorded. This provides considerable flexibility to the physician in obtaining IEGMs of interest while also reducing the amount of data the device itself needs to record. However, room for improvement remains. As noted, upon detection of any of the selected triggers, the device records each of the selected IEGMs. In many cases, though, the physician may be interested only in particular IEGMs upon detection of particular triggers. Accordingly, it would be desirable to provide for trigger-specific recording of cardiac signal data, i.e., it would be desirable to provide implantable medical devices that are capable of sensing and recording different IEGMs in response to different triggers. It is to this end that the invention is primarily directed.